Fatigue in Cu-Zn-Al single crystals during pseudoelastic cycling: In situ observations by SEM and optical microscopy

Abstract
Previous studies have shown that pseudoelastic cycling of Cu-Zn-Al single crystals leads to surface and bulk defects with consequences on the mechanical behavior and fracture properties of these alloys. Recently it has been shown that the number of cycles to nucleate surface defects depends on the composition of the alloy. In this work we have carried out in-situ tensile cycling experiments under direct observation by scanning electron and optical microscopy. The attention was focused on single crystals with an electron concentration of 1.43. We found strong correlation between the dynamics of the transformation-retransformation cycles and the surface and bulk defects, which form aligned with the trace of the habit plane and the basal plane of the induced martensite. In addition, the orientation of the tensile axis was found to be an important parameter concerning the morphology of the surface defects. Transmission electron microscopy studies have been performed to complete the characterization of defects.